This invention relates generally to cellular telecommunications systems and, more particularly, to satellite-based cellular telecommunications systems.
The use of mobile cellular telephones has proliferated in the many large metropolitan areas in which cellular telecommunications systems have been installed. Cellular telecommunications systems provide voice communications between a mobile telephone user and fixed telephone users or to other mobile telephone users, as well as data communications for mobile facsimile machines and modem-equipped computers. A typical cellular telephone systems includes a grid of service zones or cells, with each cell having a base station situated near its center. A mobile telephone user located in a particular cell is connected to that cell's base station through low-power radio frequency (rf) transmissions. Each base station is connected by trunk lines to a gateway station, which is connected by trunk lines to a local and long distance telephone network.
The cellular telecommunications systems in use today are generally land-based systems that have been installed in large metropolitan areas. Small towns and rural areas cannot economically justify the installation and operation of one of these relatively costly systems. To provide cellular telephone service for these areas, satellite-based cellular telecommunications systems have been proposed which would provide world-wide cellular telephone service. These proposed cellular telephone systems typically include a large constellation of telecommunications satellites in low earth orbit at an altitude of between approximately 400 and 1000 nautical miles, which is just below the Van Allen radiation belt. At these low altitudes, as many as 50 to 80 satellites are required to provide adequate coverage of the entire earth. This results in an extremely costly and complex system with a large number of rapidly changing crosslinks and a large number of bean-to-beam and satellite-to-satellite handovers. Accordingly, there has been a need for a less costly ad complex satellite-based cellular telecommunications system. The present invention clearly fulfills this need.